1. Field of the Invention
The present invention relates generally to polymer waveguides used for light generation and reception in touch screen displays, and more particularly, to an improved lens structure for free space optical systems which maximizes the free space light coupling between transmit and receive waveguides.
2. Description of the Related Art
User input devices for data processing systems can take many forms. Two types of relevance are touch screens and pen-based screens. With either a touch screen or a pen-based screen, a user may input data by touching the display screen with either a finger or an input device such as a stylus or pen.
One conventional approach to providing a touch or pen-based input system is to overlay a resistive or capacitive film over the display screen. This approach has a number of problems. Foremost, the film causes the display to appear dim and obscures viewing of the underlying display. To compensate, the intensity of the display screen is often increased. However, in the case of most portable devices, such as cell phones, personal digital assistants, and laptop computers, the added intensity requires additional power, reducing the life of the battery in the device. The films are also easily damaged. In addition, the cost of the film scales dramatically with the size of the screen. With large screens, the cost is typically prohibitive.
Another approach to providing touch or pen-based input systems is to use an array of source Light Emitting Diodes (LEDs) along two adjacent X-Y sides of an input display and a reciprocal array of corresponding photodiodes along the opposite two adjacent X-Y sides of the input display. Each LED generates a light beam directed to the reciprocal photodiode. When the user touches the display, with either a finger or pen, the interruptions in the light beams are detected by the corresponding X and Y photodiodes on the opposite side of the display. The data input is determined by calculating the coordinates of the interruptions as detected by the X and Y photodiodes. This type of data input display, however, also has a number of problems. A large number of LEDs and photodiodes are required for a typical data input display. The position of the LEDs and the reciprocal photodiodes also need to be aligned. The relatively large number of LEDs and photodiodes, and the need for precise alignment, make such displays complex, expensive, and difficult to manufacture.
Yet another approach involves the use of polymer waveguides to both generate and receive beams of light from a single light source to a single array detector. The waveguides are usually made using lithographic processes. One type of known polymer waveguide is made by forming a bottom cladding layer over a substrate. A second polymer layer is next formed on the bottom polymer layer and patterned using photolithography to form waveguide cores and lenses. A third polymer layer is then formed over the lenses and waveguide cores. The first and third polymer layers have the same index of refraction N1, which is lower than the index of refraction N2 of the middle or second polymer layer.
In use, a first L-shaped waveguide is positioned on the X and Y transmitting sides of a display surface. A second L-shaped waveguide is positioned on the opposite or receiving X and Y sides of the display surface. The lenses of the first waveguide, which are coupled to a light source through the individual waveguide cores, are arranged to generate either a grid or lamina of collimated light across the display surface. The lenses of the second waveguide are optically coupled to each of the lenses on the transmit side of the display. When a data entry is made on the touch screen, using a finger or pointing instrument such as a pen or stylus, an interruption occurs in the grid or lamina of light. An optical sensor, coupled to the individual waveguide cores on the receive side, is able to detect the data entry based on the X, Y coordinates of the interruption.
For more details making and using polymer waveguides, see for example, U.S. application Ser. No. 10/861,251 entitled “Apparatus and Method for a Molded Waveguide for Use with Touch Screen Displays”, filed Jun. 4, 2004, U.S. application Ser. No. 10/862,003 entitled “Waveguide With Three-Dimensional Lens” filed Jun. 4, 2004, U.S. Ser. No. 10/862,007 entitled “Techniques for Manufacturing a Waveguide with Three Dimensional Lens” filed Jun. 4, 2004, U.S. application Ser. No. 10/758,759 entitled “Hybrid Waveguide” filed Jan. 15, 2004, and U.S. application Ser. No. 11/498,356 entitled Apparatus and Method for Singulation of Polymer Waveguides Using Photolithography” filed Aug. 2, 2006, all assigned to the assignee of the present invention and each incorporated by reference herein for all purposes. The specification of U.S. application Ser. No. 11/498,356 is attached herewith as Appendix A.
Currently known polymer waveguides have only a single refractory lens surface provided at the end of each waveguide core. These lenses are typically two dimensional, meaning they are capable of collimating light in the only the X and Y planes. Since it is difficult to fabricate a three dimensional polymer lens using photolithography, current polymer waveguides do an inadequate job in collimating light in the Z plane. As a consequence, single lens optical waveguides have poor optical coupling in the Z plane.
To compensate for the poor coupling in the Z plane, a precision molded “vertical” lens is used in cooperation with polymer waveguide. The precision molded lens includes a support area to support the polymer waveguide. When positioned on the support, the vertical lens is optically aligned with the lenses on the waveguide. The combined polymer waveguide and vertical lens generates a free space optical beam directed and collimated in the Z as well and the X, Y planes.
Problems arise with the aforementioned arrangement due to alignment issues. The accurate projection (transmit) and coupling (receive) of the light from the transmit polymer waveguide to the receive polymer waveguide is critically influence by the accurate placement of transmit and receive waveguides relative to the focal point of the vertical lens. In other words, if the polymer waveguides are not precisely aligned with their respective vertical lenses, it may result in the loss of optical coupling between transmit and receive waveguides. For example if there a misalignment issues on the receiving end, then it is likely that the focal point of the vertical lens will fall outside the lenses of the polymer waveguide. The amount of light coupling will therefore be significantly reduced. As a general rule, a slight misalignment will often cause a rather dramatic loss of optical coupling or power at the receiving waveguide.
Accordingly, there is a need for a polymer waveguide assembly having a two lens vertical structure to collimate in the Z plane so light received in free space and exiting the two lenses is substantially within the acceptance angle of the waveguide, allowing a significantly lower sensitivity of optical coupling efficiency with waveguide alignment, thereby minimizing problems caused by misalignment and improving optical coupling.